Patent GB-592846-A (GB)
Title: Telecommunication systems
IPC: H04Q1/18
Filed: 1944-03-31
Abstract: 592,846. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. March 31, 1944, No. 6002. Convention date, April 23, 1943. [Class 40 (iv)] [Also in Group XXXVIII] An automatic exchange system which uses power-driven switches preferably of the kind described in Specifications 558,416 and 563,501, in which the wiper carriage moves in a straight line and co-operates with different terminals on the forward and return journeys, the wipers, other than the test wiper, making contact with their terminals only when the switch stops, also uses the multi-potential marking method of control described in Specification 573,405. In this method, a pair of potentials characteristic of a desired selection, e.g. that of a calling line, of an idle line in a particular group or of a wanted line are applied to the grids of a pair of thermionic tubes having a common cathode (or having their cathodes connected together directly or through a fixed potential source) and the cathode circuit is connected to the test wiper of the switch being controlled. When the wiper encounters a potential that matches the pair of grid potentials, the difference in the anode currents of the two tubes is such as to cause a discharge in a cold-cathode tube and the operation of a relay which stops the switch. In an alternative arrangement, the tubes have different characteristics and their grids are given the same potential. This test equipment is situated in an allotter for controlling the first finders and in a non-translating register controller for controlling the second finders and the numerical switches. The control of ringing and the transmission of busy tone takes place from a non-numerical link by which the register controller is associated with the second finder/first selector link. In the result, all the other numerical switches have substantially identical circuits which involve only two relays each. The first finder has a similar circuit, but involves two additional relays, one of which is for controlling line identifying apparatus by which the number of a faulty or a calling line may be shown on a number indicator to a local wire chief or to a distant toll operator. In the case of outgoing calls, the register-controllers send impulses over the outgoing loop in the usual way. Incoming junctions, which may be from similar " Universal " offices or from Strowger or Rotary offices have access to special register controllers. When these are seized by a junction from a Rotary office, they adapt their circuits to revertive control of their registers by the distant registers. When they are seized by a Strowger junction, the first digit is taken by an impulse regenerator in the incoming circuit and the register controllers adapt their circuits so that they may respond to the first two digits simultaneously. First call-finder. Line relay LR, Fig. 6, energizes the starting relay ASR in the common control and allotter circuit, Fig. 7, over wire X and applies the calling potential to the tterminals in the finders, Fig. 5, and combined finder-final selectors, Fig. 5b. ASR connects to the grids of a twin control tube V co-operating with a cold-cathode tube GV as described in Specification 573,405 the potentials suitable for the control of the allotter, the clutch magnet PA of which is energized in series with a relay QBR, and connects the cathode to the allotter t-wiper. When an idle finder is reached, the firing of GV energizes GVR which is followed by GSR. This disconnects QBR and the clutch magnet and extinguishes GV and GVR falls and is followed shortly afterwards by GSR. In the meantime, however, FR has pulled up and locked to change the potentials on the grids of the twin control tube to those suitable for the control of the finder. The relapse of the clutch magnet brings the selector brushes A ... G into contact with their terminals as described in Specification 558,416. QBR, on falling, grounds the t-wire, FR energizes XR in the selected finder and thus is followed by BR, Fig. 5 or 5b. GSR on falling, energizes GR which connects the cathode of the twin control tube to a-wire to the finder and energizes AR in the latter over the b-wire. AR connects up the finder clutch magnet P and connects the a-wire to the t wiper and the finder then hunts in the same way as the allotter. When the line is found, GVR, GSR operate as before and AR and the clutch magnet fall back. GSR also energizes ER which locks and connects ground and battery over a retard coil to the a- and b-wires. On the relapse of the finder clutch magnet, the a, band c brushes make contact with their terminals and cut off relay COR is operated. Overfiow arrangements are described in a separate paragraph. Associating second finder with register controller. Relay FR in the allotter circuit energizes BSR1, Fig. 9, which is common to the group of links for associating register-controllers with the second finders, and marks the tterminals of all the idle first-choice second finders in the upper switches of these links and energizes their clutch magnets PL. The switches hunt in known manner under control of relays TIR, T2R. The latter in the successful link energizes the clutch magnet PR of the registercontroller selector which hunts in a similar manner under the control of relays T3R, T4R. The latter energizes RAR in the registercontroller, Figs. 10, 10a and 10b, and DCR, Fig. 9, which switches the link through to the register-controller and causes the operation of LAR, SIR, LRR in the selected second finder, the a- and b-wires from which are now connected to the impulse relay DR in the register-controller. On the operation of LRR, T1R and T2R fall back. Control of second finder by register-controller. RAR in the register-controller operates RBR which connects the cathode of a twin-tube V1 similar to V in the allotter circuit to the a-wire from the finder and over the b-wire energizes AR1 to operate the clutch magnet P1. When the t-wiper encounters the potential of a calling first finder (via wiper D in the allotter GV1 fires and GVR1 stops the finder and energizes GSR1 which energizes RCR, releases GVR1 and then falls back. RCR locks and releases RBR which connects the impulse relay DR to the a- and b-wires again and, since these wires are bridged through resistance R1, Fig. 7, DR now operates. When the second finder switches through, JR operates in the allotter and with JR and ER both operated, ASR falls followed by the rest of the allotter relays, the switch remaining in its present position until it is driven on by a new call. DR is now held over the subscriber's loop. Registering wanted number. The register switches ED1 ... ED6 and the in and out sequence switches E1, E0 are escapementcontrolled switches, e.g. of the type described in Specification 559,411, driven by a common power shaft and are arranged at each step to operate a relay such as PCR2 which interrupts the circuit of the escapement magnet and locks up until the end of the operating impulse. When the register-controller is taken into use, relays RAR, RCR, RXR, RIR, DR are operated and the in-sequence switch goes to position 1 and sends back dialling tone. The digits are registered in the usual way, the relapse of series relay R2R after each causing the in-sequence switch to step on. In the case of local calls, however, since they involve only six digits, the sequence switch skips position 4. Controlling selectors in local call. The digit registers (except the tens register ED6) apply potentials corresponding to the digits in succession to the grids of control tube V1. When the first register ED1 goes off-normal, a circuit is made over its C-bank and that of the outsequence switch EO for RSR, PRR. This connects the cathode of the tube via wire f, Figs. 9 and 8, to the a-wire of the first selector and causes the energization of AR2 and the operation of the clutch magnet therein. The switch advances until it encounters the potential characteristic of an idle line in the selected group. GV1 then fires and GVR1 releases RSR, AR2 and the switch stops. When the a, band c brushes make contact, BR in the second selector, Fig. 5, pulls up in series with LBR which remains unoperated. RT1R in the register-controller now pulls up over the a-wire and resistance R1 of the selector and shunts its high-resistance winding by a low resistance winding in series with RT2R to guard against double connections. If these relays remain up, the relapse of GVR1 when GSR1 comes up steps on the out-sequence switch. If there is a simultaneous test and the other switch is successful in holding the trunk, RT2R fails to come up and a circuit is made for DAR, Fig. 9, which releases the connection so far set up and the register-controller and sends back busy tone. The remaining group selectors are controlled similarly. When the tens register steps off normal, RGR operates (via bank F of the out-sequence switch) with RSR and releases PRR. AR is operated in the final selector, Fig. 5b, and the switch moves off, but in this case the tube V1 is ineffective and the test potentials found by the final selector on each group terminal are undifferentiated and causethe firing of a second tube V2 and consequent momentary operation of GVR2, GSR2. This does not release RSR or stop the selector, but gives a step to a counter switch EC, Fig. 10b. When the latter reaches a position one step short of the value of the dialled tens digit, a circuit is made for RFR which holds RGR and transfers the stepping circuit from EG to EO which thus moves to its last position when the final selector reaches the selected group terminal. With RFR up, operation of GVR2 releases RSR and the switch stops. RSR is not re-operated to initiate the final movement of the selector until the units digit has been completely received. The grids of V1 are then connected to potentials characteristic of the dialled units digit and the switch is stopped when it fi